Several homogeneous and heterogeneous processes based on rhodium or palladium metal catalysts have been proposed and are now being used to hydrogenate carbon-carbon double bonds in acrylonitrile-butadiene copolymers and other similar polymers.
For example, French Pat. No. 2,421,923 discloses the partial hydrogenation of the double bonds in acrylonitrile-butadiene rubber (NBR) over a palladium/charcoal catalyst.
German Offenlegungsschrift No. 3,046,008 discloses the selective hydrogenation of the double bonds in conjugated diene containing polymers such as NBR, wherein the catalyst is palladium and at least one other element on a support which may be silica, alumina or activated carbon.
German Offenlegungsschrift No. 3,046,251 discloses a similar process except that the catalyst support is channel or furnace carbon black.
Published British Patent Application No. 2,070,023A discloses a process for the selective hydrogenation of the double bonds in unsaturated organic polymers such as acrylo-nitrile-butadiene-styrene polymers, when in the form of an aqueous emulsion, using a catalyst such as chloro-tris(triphenylphosphine)rhodium in a hydrocarbon solution.
U.S. Pat. No. 3,898,208 describes a process for hydrogenation of latexes of oil-insoluble polymers of conjugated dienes. The latex is dispersed in a swelling agent for the polymer and hydrogenated in the presence of a catalyst complex which may be a rhodium complex catalyst such as chlorotris(triphenylphosphine)rhodium. The swelling agent must also be a solvent for the catalyst complex.
U.S. Pat. No. 3,700,637 discloses that the double bonds in alternating copolymers of conjugated dienes and unsaturated nitriles may be hydrogenated using catalysts which preferably are homogeneous rhodium halide complex catalysts having the formula L.sub.3 RhX wherein X is halogen and L is an organophosphorus or organoarsenic stabilizing ligand. It is also preferred that an excess of the ligand be used during the hydrogenation, the mole ratio of ligand to rhodium complex being between about 10:1 and about 150:1.
British Pat. No. 1,558,491 discloses the hydrogenation of the double bonds in copolymers of a conjugated diene and an .alpha.,.beta.-unsaturated carboxylic acid or derivative thereof, for example acrylonitrile, using as catalyst a homogeneous monovalent or trivalent rhodium halide complex of the formula L.sub.3 RhX.sub.n wherein X is chlorine or bromine, n is 1 or 3, and L is a ligand. An additional 5 to 25 weight percent, based on the copolymer of the ligand may optionally be used. The amount of hydrogenation is highly solvent dependent.
U.S. Pat. No. 3,480,659 describes a process for the selective hydrogenation of double bonds in unsaturated monomers containing 2 to 20 carbon atoms using a homogeneous rhodium hydride complex catalyst, for example, hydridotetrakis(triphenylphosphine)rhodium, along with an excess of a complexing ligand, for example triphenylphosphine. The mole ratio of ligand to catalyst is between about 10:1 and about 150:1.
Italian Pat. No. 912,648 discloses that cycloalkadienes and alkadienes may be selectively hydrogenated to the corresponding cycloalkenes and alkenes using a catalyst such as hydridotetrakis(triphenylphosphine)rhodium.
More recently, there issued U.S. Pat. Nos. 4,464,515 and 4,503,196 in which one of us is named as an inventor. U.S. Pat. No. 4,464,515 describes the hydrogenation of carbon-carbon double bonds in copolymers of conjugated dienes and copolymerizable monomers in the presence of a monovalent rhodium hydride complex of the formula RhHL.sub.1x in which x is 3 or 4 and L.sub.1 is a first ligand, a second ligand compound L.sub.2 and a solvent for the compound. U.S. Pat. No. 4,503,196 describes the selective hydrogenation in the absence of added ligand and in the presence of a monovalent rhodium hydride complex of the formula RhHL.sub.x where, when x is 4, L is a phosphorus compound which is 5-phenyl-5H-dibenzophosphole or a compound of formula PR.sub.1 R.sub.2 R.sub.3 or, when x is 3, L is an arsenic or antimony compound of the formula MR.sub.1 R.sub.2 R.sub.3, wherein M is arsenic or antimony, and wherein R.sub.1, R.sub.2 and R.sub.3 are selected from CH.sub.3, C.sub.2 H.sub.5, C.sub.6-10 aryl groups and C.sub.7-12 aralkyl groups.
The advantage of the processes described in the latter two patents is that improved rates of hydrogenation are achieved under relatively mild conditions and that the degree of hydrogenation is relatively insensitive to the amount of solvent used.
However, rhodium is an expensive metal and hence we made an investigation to look for an efficient but cheaper hydrogenation process based on other catalyst materials.
In U.S. Pat. No. 4,631,315, there is described the hydrogenation of nitrile group-containing polymers in a low molecular weight ketone as a solvent using certain ruthenium catalysts having the formula: EQU RuX[(L.sub.1)(L.sub.2).sub.n ]
wherein X represents hydrogen or halogen, L.sub.1 represents hydrogen, halogen or optionally substituted cyclopentadienyl, L.sub.2 represents phosphine, bisphosphine or arsine, n is 1, 2 or 3 and [(L.sub.1)(L.sub.2).sub.n ] represents a cyclopentadienyl bisphosphine. The data presented in this patent suggests that free ligand is necessary to achieve acceptable reaction rates.
In published German patent application No. 3,529,252, there is also described the hydrogenation of nitrile group-containing polymers in a low molecular weight ketone using other ruthenium catalysts, this time of the formula: EQU RuH.sub.m (COOR.sub.1).sub.n (L).sub.p
wherein R.sub.1 is an alkyl, aryl, cycloalkyl or aralkyl, L represents phosphine or arsine, m is 0 or 1, n is 1 or 3 and p is 2 or 3.